<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <style>
        .sky{
            width: 100px;
            height: 100px;
            background-color: green;
            margin-bottom: 60px;
        }
        .moon{
            width: 50px;
            height: 50px;
            background-color: red;
            margin: 10px;
            /*【1】在子元素的外边距是可以看到父盒子的背景色的。*/
        }
        .sky1{
            /*【2】这里发生了边距合并，sky1的子盒子和sky1的合并，sky1和sky的合并*/
            margin-top: 70px;
            width: 100px;
            height: 200px;
            background-color: green;
        }
        .moon1{
            width: 40px;
            height: 40px;
            margin: 50%;
            margin-bottom: 60%;
            background-color: yellow;
        }
    </style>
</head>
<body>
<div class="sky">
    <div class="moon">

    </div>
</div>
<div class="sky1">
    <div class="moon1">

    </div>
</div>
</body>
</html>